PS：在CentOS下運作yum install flash-plugin或yum install mplayer的時候，提示庫裡沒有找到這個軟體？為什麼會這樣？因為CentOS是RHEL編譯過來的，去掉了所有關于版權問題的東西。是以，在沒有使用第三方軟體庫的情況下，很多軟體無法用yum install來直接安裝。
EPEL(Extra Packages for Enterprise Linux )軟體庫提供為 EL4 及 EL5 重新編譯的 Fedora 元件。這個軟體庫在不替換系統元件方面下了功夫。在某些情況下它嘗試直接針對 CentOS 相容性的問題，但堅決否定軟體庫間的相容性是目标之一。當它與其它第三方軟體庫混合使用時，問題可能會出現。故此，當你使用 EPEL 時，尤其是當你亦會運用其它件庫的元件時，請確定你使用 yum 的 Priorities 插件。
RPMForge庫現在已經擁有超過10000種的CentOS的軟體包，被CentOS社群認為是最安全也是最穩定的一個第三方軟體庫。
下面，偶就來講解下如何使用EPEL與RPMForge、RPMFusion軟體倉庫：
一、安裝yum-priorities插件。
這個插件是用來設定yum在調用軟體源時的順序的。因為官方提供的軟體源，都是比較穩定和被推薦使用的。是以，官方源的順序要高于第三方源的順序。如何保證這個順序，就需要安裝yum-priorities這插件了。
[[email protected] ~]# yum install yum-priorities #安裝yum-priorities 安裝完後需要設定/etc/yum.repos.d/ 目錄下的.repo相關檔案（如CentOS-Base.repo），在這些檔案中插入順序指令：priority=N （N為1到99的正整數，數值越小越優先）
一般的配置是這樣的：
[base], [addons], [updates], [extras] … priority=1
[CentOSplus],[contrib] … priority=2
其他第三的軟體源為：priority=N （推薦N>10） 如我的CentOS-Base.repo配置為：
# CentOS-Base.repo
#
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client. You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
#
#
[base]
name=CentOS-$releasever – Base
mirrorlist=http://mirrorlist.CentOS.org/?release=$releasever&arch=$basearch&repo=os
#baseurl=http://mirror.CentOS.org/CentOS/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
priority=1
#released updates
[updates]
name=CentOS-$releasever – Updates
mirrorlist=http://mirrorlist.CentOS.org/?release=$releasever&arch=$basearch&repo=updates
#baseurl=http://mirror.CentOS.org/CentOS/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
priority=1
#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever – Addons
mirrorlist=http://mirrorlist.CentOS.org/?release=$releasever&arch=$basearch&repo=addons
#baseurl=http://mirror.CentOS.org/CentOS/$releasever/addons/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
priority=1
#additional packages that may be useful
[extras]
name=CentOS-$releasever – Extras
mirrorlist=http://mirrorlist.CentOS.org/?release=$releasever&arch=$basearch&repo=extras
#baseurl=http://mirror.CentOS.org/CentOS/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
priority=1
#additional packages that extend functionality of existing packages
[CentOSplus]
name=CentOS-$releasever – Plus
mirrorlist=http://mirrorlist.CentOS.org/?release=$releasever&arch=$basearch&repo=CentOSplus
#baseurl=http://mirror.CentOS.org/CentOS/$releasever/CentOSplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
priority=2
#contrib – packages by CentOS Users
[contrib]
name=CentOS-$releasever – Contrib
mirrorlist=http://mirrorlist.CentOS.org/?release=$releasever&arch=$basearch&repo=contrib
#baseurl=http://mirror.CentOS.org/CentOS/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
priority=2 二、下載下傳與安裝相應EPEL的rpm檔案包
1，下載下傳與安裝EPEL的rpm檔案包
32位系統
[[email protected] ~]# rpm -ivh http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-4.noarch.rpm 64位系統
[[email protected] ~]# rpm -ivh http://download.fedora.redhat.com/pub/epel/5/x86_64/epel-release-5-4.noarch.rpm 如果您不清楚您的系統核心，請使用 uname -a 指令來檢視您的核心資訊。
2，導入DAG的PGP Key
[[email protected] ~]# rpm –import /etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL 3，設定/etc/yum.repos.d/epel.repo檔案中源的級别，就是添加priority=11這句。
如我的epel.repo檔案内容：
[epel]
name=Extra Packages for Enterprise Linux 5 – $basearch
#baseurl=http://download.fedoraproject.org/pub/epel/5/$basearch
mirrorlist=http://mirrors.fedoraproject.org/mirrorlist?repo=epel-5&arch=$basearch
failovermethod=priority
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL
priority=11
[epel-debuginfo]
name=Extra Packages for Enterprise Linux 5 – $basearch – Debug
#baseurl=http://download.fedoraproject.org/pub/epel/5/$basearch/debug
mirrorlist=http://mirrors.fedoraproject.org/mirrorlist?repo=epel-debug-5&arch=$basearch
failovermethod=priority
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL
gpgcheck=1
[epel-source]
name=Extra Packages for Enterprise Linux 5 – $basearch – Source
#baseurl=http://download.fedoraproject.org/pub/epel/5/SRPMS
mirrorlist=http://mirrors.fedoraproject.org/mirrorlist?repo=epel-source-5&arch=$basearch
failovermethod=priority
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL
gpgcheck=1 三、下載下傳與安裝相應rpmforge的rpm檔案包
1，下載下傳rpmforge的rpm檔案包
32位系統
[[email protected] ~]# wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.2-2.el5.rf.i386.rpm 64位系統
[[email protected] ~]# wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.2-2.el5.rf.x86_64.rpm 2，安裝DAG的PGP Key
[[email protected] ~]# rpm –import http://dag.wieers.com/rpm/packages/RPM-GPG-KEY.dag.txt 3，驗證rpmforge的rpm檔案包
[[email protected] ~]# rpm -K rpmforge-release-0.5.1-1.el5.rf.*.rpm 4，安裝rpmforge的rpm檔案包
[[email protected] ~]# rpm -i rpmforge-release-0.5.1-1.el5.rf.*.rpm 5，設定/etc/yum.repos.d/rpmforge.repo檔案中源的級别，就是添加priority=12這句。
如我的rpmforge.repo檔案内容：
### Name: RPMforge RPM Repository for Red Hat Enterprise 5 – dag
### URL: http://rpmforge.net/
[rpmforge]
name = Red Hat Enterprise $releasever – RPMforge.net – dag
baseurl = http://apt.sw.be/redhat/el5/en/$basearch/rpmforge
mirrorlist = http://apt.sw.be/redhat/el5/en/mirrors-rpmforge
#mirrorlist = file:///etc/yum.repos.d/mirrors-rpmforge
enabled = 1
protect = 0
gpgkey = file:///etc/pki/rpm-gpg/RPM-GPG-KEY-rpmforge-dag
gpgcheck = 1
priority=12 四、下載下傳與安裝相應rpmfusion的rpm檔案包
（CentOS官方說這個軟體庫裡面的軟體穩定性不如rpmforge，選用！rpmfusion官方站：http://rpmfusion.org）
[[email protected] ~]# rpm -Uvh http://download1.rpmfusion.org/free/el/updates/testing/5/i386/rpmfusion-free-release-5-0.1.noarch.rpm
[[email protected] ~]# rpm -Uvh http://download1.rpmfusion.org/nonfree/el/updates/testing/5/i386/rpmfusion-nonfree-release-5-0.1.noarch.rpm 五、測試
1，測試更新
[[email protected] ~]# yum check-update 輸出資訊應該會有以下兩行：
Loading “priorities” plugin
…
XX packages excluded due to repository priority protections
2，安裝下mplayer播放器試試，如果安裝成功了就沒有問題了。
[[email protected] ~]# yum install mplayer PS：以上配置在RHEL/CentOS 5.X所有系列都可以使用！由本人驗證總結整理。
參考文檔：http://wiki.centos.org/zh/AdditionalResources/Repositories/RPMForge
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